The Third Generation Project Partnership (3GPP) has developed the System Architecture Evolution (SAE) as the core network architecture of its future and Long Term Evolution (LTE) wireless mobile telecommunications standard. The main component of the SAE architecture is the Evolved Packet Core (EPC). The LTE/SAE network includes network entities supporting the user and control planes.
A Serving Gateway (SGW) routes and forwards user data packets and acts as an anchor for mobility between LTE and other 3GPP technologies. It also manages and stores User Equipment (UE) contexts, e.g. parameters of the IP bearer service and network internal routing information. A Public Data Network gateway (PDN-GW or PGW) provides connectivity from the UE to external PDNs by being the point of exit and entry of traffic for the UE. The PGW also performs policy enforcement and other functions and acts as the anchor for mobility between 3GPP and non-3GPP technologies. As used herein, the term UE is intended to refer to any piece of equipment that is configured to access the internet, and would include, for example and without limitation, mobile telecommunication devices, portable or handheld computing devices and desktop or installed computers.
The 3GPP and Broadband Forum (BBF) have been developing Fixed Mobile Convergence (FMC), for seamlessly providing LTE services to Broadband Internet users. For this, the 3GPP Release 8 standard defines three ways to connect non-3GPP accesses to the EPC, named as S2a, S2b and S2c after the key interfaces. These are shown in FIG. 1, which illustrates the key entities and network paths involved between a UE 10 and a mobile access network with EPC components 31. As illustrated in FIG. 1 UE 10 connects to a Broadband network, in this example a Broadband Home Network 12, and then via a BBF-defined access network 20 to the Evolved Packet System 30. Also shown are other equipment entities that connect to the Broadband Home Network 12, such as a WiFi AP 13, a TV 14 with set-top box 15, a personal computer 16, a Media centre 17 and a printer 18.
A Residential gateway (RG) 19 in the Broadband Home Network 12 connects to an access node (AN) 21 in the BBF-defined access network 20, which in turn connects to a Border Network Gateway (BNG) 22. Other entities in the BBF-defined access network 20 that connect to the BNG 22 include a Broadband, or BBF, Policy Control Function (BPCF) 23, a BBF Authorisation and Accounting server (BBF AAA) 24 and other fixed operator services 25.
In the Evolved Packet System 30 is a PDN-GW 32, to which user data packets are sent by one of the three methods S2a, S2b, S2c. In addition, the Evolved Packet System 30 includes the mobile access network with EPC components 32, accessed via a Serving Gateway 33, a Policy and Charging Rules Function (PCRF) 34, a 3GPP Authorisation and Accounting server (3GPP AAA) 35, a user's Home Subscriber Server (HSS) 36, a Security Gateway (SeGW) 37 and other entities 38 for the Operator-provided IP services. For some accesses an Evolved Packet Data Gateway (ePDG) may be provided between the PDN-GW 32 and the external gateway node (in this case the BNG 22).
FMC-defined S2c accesses use the Dual-Stack Mobile IPv6 (DSMIPv6) protocol, which sets up a tunnel between the UE 10 and the PDN-GW 32. This is not attractive to many operators for a variety of reasons, including fears that there could be Intellectual Property rights issues regarding use of DSMIPv6.
S2b accesses work by assigning a local IP address to the UE 10 in the BBF network. Then, using this address, the UE 10 connects to the EPC via the ePDG 36 using an IPsec tunnel. For this purpose the UE 10 receives a second IP address, assigned by the EPC. This mode of operation allows the UE 10 to use the second IP address for communication via the EPC to, for example, the service network 38 of the operator (for example, for sending/receiving MMS messages); or as another example to the internet through the operator's firewall and/or online charging systems.
S2a accesses operate without any tunnelling in the UE 10. The BBF network 20 recognizes the UE 10 during authentication and, if the home network of the UE 10 prescribes, the BBF network 20 (specifically the BNG 22) will forward the user's data packet traffic to the EP System 30. The UE 10 sees a native connectivity to the EPC; has only one IP address (provided by the EPC); needs to perform no extra signalling or set up any tunnel; and can send IP packets directly encapsulated in the Wireless Local Area Network (WLAN) frame, which IP packets are routed through the EPC. There are several benefits of S2a, the key one being that no extra features are required in the UE to provide basic EPC connectivity. Simply turning WLAN on in an iPhone, for example, can enable the user to connect to the EPC.
However, for more advanced features, such as mobility between 3G/LTE and WLAN or opening multiple parallel PDN connections, the S2a access method would require some modifications in the UE. A key drawback with S2a is that all PDN accesses, including local nodes or the internet involves routing via the EPC. Since the UE is provided with only a single IP address, it is not possible to control which transport sessions to route through the EPC, or to select between accessing a local network and accessing a PDN via the EPC, as is the case with S2b accesses (and, in fact also with S2c accesses).
One possible solution that has been proposed is to add controls to the S2a access method, which allow the traffic of the UE to be routed either through the EPC (together with assigning an EPC IP address to the UE) or to be routed locally (by assigning a local IP address). However, such controls allow only that either all the UE's traffic is routed via the EPC or all is routed locally. Other proposals have suggested allowing the BNG to decide which traffic flows to route through the EPC and which to route locally. However, this requires a network address translation (NAT) function in the BNG. Also, even if the UE is extended to support multiple PDN connections, in these proposed solutions the routing of each of the PDN connections can only be selected by the network operator, meaning that the UE itself would not be involved and completely unaware which route its traffic was taking. Thus S2a, in spite of its advantages has some drawbacks when compared to the S2b and S2c access methods, where local communication in parallel with communication via the EPC is readily available.